Japan raises Fukushima nuclear crisis alert rating to 5 on scale of 7

Source: International Atomic Energy Agency

Japanese authorities have raised the alert level for events at Units 2 and 3 of the Fukushima Daiichi nuclear complex to five on the International Nuclear and Radiological Events Scale (INES) seven point safety significance rating, reports the International Atomic Energy Agency (IAEA).

General Description of INES LevelsThe adjusted INES rating now labels the issues at Units 2 and 3 of Fukushima Daiichi complex as an “Accident with wider consequences,” the same rating applied to the U.S. Three Mile Island nuclear accident in 1979.

For comprehensive coverage of the Japanese nuclear power disaster and efforts under way to resolve it, visit PennEnergy’s Japan Earthquake and Nuclear Emergency 2011 special section. 

As concerns increase over the spent fuel storage conditions at the Fukushima nuclear complex Japanese authorities expanded their efforts to stabilize temperatures with a series of water drops from helicopters and trucks onto the Unit 3 reactor building Thursday.

Engineers also continued work to connect an external power cable to the Unit 2 reactor at the Fukushima nuclear complex, which would allow cooling pumps to be restarted.

Conditions at the Unit 4 reactor remain a major safety concern. Japanese authorities informed the IAEA that prior to the earthquake the entire fuel core at the Unit 4 reactor of the Fukushima Daiichi nuclear complex had been unloaded and placed in the spent fuel pond located in the reactor's building.

Spent fuel removed from a nuclear reactor is highly radioactive and generates intense heat. Nuclear plant operators typically store this material in pools of water that cool the fuel and shield the radioactivity. Water in a spent fuel pool is continuously cooled to remove heat produced by spent fuel assemblies. According to IAEA experts, a typical spent fuel pool temperature is kept below 25 °C under normal operating conditions. The temperature of a spent fuel pool is maintained by constant cooling, which requires a constant power source.

Given the intense heat and radiation that spent fuel assemblies can generate, spent fuel pools must be constantly checked for water level and temperature. If fuel is no longer covered by water or temperatures reach a boiling point, fuel can become exposed and create a risk of radioactive release. The concern about the spent fuel pools at Fukushima Daiichi is that sources of power to cool the pools have been compromised.

The IAEA also outlined in its recent updates that Japan's Nuclear and Industrial Safety Agency reported increasing temperatures in the spent fuel ponds at Units 5 and 6 since March 14. An emergency diesel generator at Unit 6 is now powering water injection into the ponds at those Units.

The IAEA can confirm the following new information regarding the temperatures of the spent nuclear fuel pools at Units 4, 5 and 6 at Fukushima Daiichi nuclear complex:

Unit 4 March 13, 19:08 UTC: 84 °C
Unit 5 March 17, 03:00 UTC: 64.2 °C March17,18:00 UTC: 65.5 °C
Unit 6 March 17, 03:00 UTC: 62.5 °C March 17, 18:00 UTC: 62.0 °C

The IAEA also clarified that contrary to several news reports, the agency to date has not received any notification from the Japanese authorities of people sickened by radiation contamination.

The IAEA is continuing to seek further information about the water levels, temperature and condition of all spent fuel pool facilities at the Fukushima Daiichi nuclear power plant.

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